Solid-Phase Synthesis of Thio-oligosaccharides

No protecting groups are present in the highly reactive polymer-bound sugar 1-thiolates 1 , which undergo reactions with sugar triflates 2 to give thio-oligosaccharides 3 in high yield. Tr=trityl=triphenylmethyl, Tf=trifluoromethylsulfonyl, Bz=benzoyl.     

糖苷和寡糖的立体选择性合成研究进展

精苷、寡糖的立体选择性合成是一个十分重要的课题. 本文结合作者的研究工作介绍了糖苷、寡糖的立体选择合成的方法学进展,主要涉及近年来合成寡糖的新方法,并对这些方法的优势及不足进行了评述.     

First Synthetic Carbohydrates with the Full Anticoagulant Properties of Heparin

A single disaccharide building block is required to obtain synthetic carbohydrates that reproduce the anticoagulant activity of heparin and inhibit thrombin (n>6) and/or factor Xa (n≥2; see reaction scheme). Thus, there is evidence that heparin fragments with at least 15 saccharide units are required for thrombin inhibition. Lev=levulinoyl.     

Quantitative Monitoring of Solid-Phase Synthesis Using Gated Decoupling 13C NMR Spectroscopy with a 13C-Enriched Protecting Group and an Internal Standard in the Synthesis of Sialyl LewisX Tetrasaccharide

Just tagging along. For the nondestructive quantitative monitoring of solid-phase oligosaccharide synthesis a ¹³C-enriched tag (*) was incorporated in the linker and a ¹³C-enriched protecting group (⧫) was included in the growing molecule. By integration of the signals in a gated decoupling ¹³C NMR experiment the reaction progress can be monitored. This method was demonstrated with the synthesis of sialyl Lewis^x tetrasaccharide on a Tentagel support ((P)). Bn=benzyl, PEG=poly(ethylene glycol).     

A Comparative Study of Glycosyl Thioimidates as Building Blocks for Chemical Glycosylation

Our results indicate that the reactivity and the activation profile of thioimidate glycosyl donors vary significantly depending on the endocyclic heteroatom (N,O,S). Reactivity diminishes in accordance with the following sequence: O > S > N; and this trend stands for a majority of promoters tested. Acyclic glycosyl thioimidates were found to be generally less reactive than the respective cyclic counterparts. The difference in the reactivity was confirmed in direct competition experiments. These findings made possible a two-step one-pot selective activation using thioimidates as the anomeric leaving group of the glycosyl donor and temporary masking group of the glycosyl acceptor.

Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Carbohydrate Chemistry to view the supplemental file.     

Capillary electrophoresis as a method to determine underivatized urinary lipoarabinomannans,a biomarker of active tuberculosis caused by Mycobacterium tuberculosis

Tuberculosis is a devastating contagious disease caused by Mycobacterium tuberculosis. This is the first report describing the development of novel capillary electrophoresis methods to detect lipoarabinomannans shed into the blood circulation by replicating bacteria. The novelty of the methods is the detection without derivatization. The lipoarabinomannan is detected owing to the ionization of the diverse functional groups of the structure, such as the multibranched mannan domain or the phosphatidyl group. Four alkaline solutions were used; normal polarity in three of them and reversed polarity in one. Urinary lipoarabinomannans by saccharide domains were identified with direct absorbance detection. The accuracy and the analytical sensitivity were then validated with cello‐, manno‐ and xylooligosaccharides. Lipoarabinomannan detection was feasible within 20 min (RSD 2.1%). This method worked at the dynamic range of 0.1–10 μg/mL. With reversed polarity, indirect absorbance detection, and pH 9.0 electrolyte were used, the analytes migrated already within 5 min (RSD 0.01%). Inorganic nonabsorbing ions were used for this method optimization. This improvement resulted in the detection limit of 1 pg/mL in water and in the linear dynamic range of 1 pg/mL to 10 ng/mL. In conclusion, the described method has great potential as a point‐of‐care assay for clinical use.     

Synthesis of Differentially Protected Glucosamine Building Blocks and Their Evaluation as Glycosylating Agents

The modular assembly of heparin oligosaccharides requires glucosamine building blocks with amine protecting groups for α-selective glycosylations that can be readily removed. The synthesis of N-4-nitrobenzensulphonamide (nosyl)- and N-2,4-dinitrophenyl (DNP)-protected glucosamine building blocks and their evaluation as glycosylating agents is described. The N-nosyl-protected glucosamine building blocks were challenging to prepare and their glycosylations resulted in inseparable mixtures of products. The N-DNP-protected glucosamines, however, were readily synthesized and resulted in α-selective couplings to protected l-iduronic acid derivatives.     

Mass Spectrometry of Oligosaccharides(I)—Formation of the [M+Nh4]+ Ion of Oligosaccharides in Fast Atom Bombardment Mass Spectrometry

In positive-ion fast atom bombardment (FAB) mass spectrometry, when oligosaccharides are mixed with an appropriate amount of NH₄Cl, a highly abundant [M+NH₄]⁺ peak appears in FAB mass spectra. From the adduct ion [M+NH₄]⁺, the molecular weights of oligosaccharides can be determined definitively. This technique may especially be applied to analyze the mixture of oligosaccharides.     

The Tmsotf-Promoted “One Pot” β-Glycosidations of Peracetylated Chitobiose

Abstract

β-Glycosidations of peracetylated chitobiose with such alcohols as methyl, allyl, benzyl, isopropyl, tert-butyl alcohol and 1,2:3,4-O-diisopropylidene-1-O-α-D-galactoside were carried out in good yields by employing TMSOTf as a promoter. The reaction proceeded through the oxazoline intermidiate.     

Aspects of Periodate Oxidation of Carbohydrates for the Analysis of Pyrolysis Liquids

Periodate oxidation of carbohydrates in acid, neutral, and alkaline media has been studied in order to develop a simple and fast determination method of sugars and their derivatives, such as levoglucosan, in fast pyrolysis liquids. The carbohydrates oxidized are as follows: D-glucose, D-cellobiose, D-cellotriose, D-fructose, D-sucrose, and levoglucosan. The reaction products have been analyzed with two methods: iodometric titration for iodate ions and potentiometric titration for formic acid.